Public bug reported:
[Impact]
On BlueField-3 DPU with linux-bluefield-6.8 kernel (based on Ubuntu 24.04
noble), creating a large number of sub-functions (SFs) via devlink (for example
1600+ `devlink port add ... flavour pcisf` instances) causes severe host memory
pressure. In the reported scenario, available memory dropped from roughly 22
GiB to about 4 GiB after creating on the order of 1685 SFs, while total used
memory rose dramatically.
The root cause is that `page_pool` uses fixed alloc-cache sizing
(`PP_ALLOC_CACHE_SIZE` / `PP_ALLOC_CACHE_REFILL`) tuned for 4 KiB pages and
NAPI/XDP behavior. On BlueField kernels (Ubuntu 24.04 Noble and Ubuntu 22.04
Jammy based kernels), each cached entry corresponds to a much larger backing
page, so the same object counts multiply the per-pool memory footprint. Many
network devices allocate page pools per queue or logical port; scaling SF count
multiplies that cost and can exhaust memory on 32 GiB systems even when traffic
is idle.
[Fix]
Cherry picking the upstream commit:
"net: page_pool: scale alloc cache with PAGE_SIZE"
The change scales `PP_ALLOC_CACHE_REFILL` (and hence `PP_ALLOC_CACHE_SIZE`,
which remains twice the refill watermark) by `PAGE_SIZE` so that cache
footprint in bytes is balanced across page sizes. On 4 KiB page builds the
values stay 64 / 128; on 16 KiB and 64 KiB pages they are reduced (16 / 32 and
4 / 8 respectively), cutting redundant cached page capacity where the old
constants were grossly oversized.
[Test Case]
Compiled tested on linux-bluefield-6.8 on master-next branch.
[Regression Potential]
Low. The change is confined to compile-time constants in
`include/net/page_pool/types.h`, and was accepted upstream.
** Affects: linux-bluefield (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2147290
Title:
Ubuntu 24.04 - Noble: Fix high memory use when scaling many SFs
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